This invention relates to improved thermosetting powder paints and more particularly pertains to polymeric glycoluril derivatives for cross-linking reactive polymers having reactive hydroxyl, carboxyl, or amide groups upon exposure to heat.
Powder paints are ordinarily manufactured from raw batch ingredients comprising resinous binders, opacifying and filler pigmentary solids, plasticizers, and other additives to provide opacity, good film properties, and adhesion to substrates. The raw batch ingredients are uniformly mixed, formed into coherent extrudate by hot extrusion, and then comminuted to form small particle powder paints which are ordinarily free flowing at normal room temperature. Powder paints usually are uniform small powders passing 325 mesh or less than about 44 microns. Powder paints contain little or no fugitive solvents and depend upon their own inherent characteristics of the powder to melt, level, coalesce, and fuse to form an attractive coherent film on the substrate. The powder must not fuse in the container and cannot be subjected to cold flow so as to maintain individual powder particles prior to use.
In recent years, thermosetting powder paints have become particularly suitable for use in commercial industrial process particularly since powder paints are essentially free of organic solvents whereby economic and social benefits are achieved by reduced air pollution, reduced energy use, and reduced health and fire hazards. Present commercial powder coatings often exhibit poor weathering properties although some expensive powder paints can obtain satisfactory weathering. Other difficulties often encountered in powder paints are caking or blocking of the powder in use and other mechanical application properties. Recently issued U.S. Pat. Nos. 4,118,437 and 4,064,191 disclose cross-linkable powder coatings wherein the cross-linking component is an alkylated glycoluril derivative.
It now has been found that an economical and substantially improved powder coating composition can be achieved by utilizing a polymeric cross-linker comprising an alkoxy methyl or methylol functional polymer produced by copolymerizing a glycoluril with a diol or another glycoluril. The polymeric glycoluril can comprise as low as 10% by weight of the thermosetting powder coating binder composition which exhibits excellent minimum tack greater than 70.degree. C. and particularly important for non-fusing and non-blocking powder coatings. These and other advantages of this invention will become more apparent by referring to the Detailed Description of the Invention.